1. Field of the Invention
This invention relates to X-ray phosphors. More particularly it relates to indium-activated yttrium phosphate.
2. Prior Art
Calcium tungstate has been widely used for many years as the phosphor for X-ray intensifying screens. The emission of calcium tungstate peaks at about 435 nanometers. The X-ray film commonly in use is a blue sensitive film with the film having a sensitivity in the 300 to 470 nanometer range. The sensitivity of the film is drastically reduced above about 470 nanometers.
Recently, Buchanan et al in RADIOLOGY 105: 185-190, October, 1972, indicated that the terbium-activated rare earth oxysulfides have a better efficiency of absorption of X-rays than calcium tungstate. They also state that a green-sensitive film is necessary to utilize the full benefits from the more efficient phosphors. Because the above oxysulfide phosphors have a higher efficiency and while the emission thereof does peak outside the sensitivity range for these phosphors, there is a sufficient overlap into the blue film sensitivity range to enable a one-half reduction in exposure to X-rays when these materials are compared to calcium tungstate.
Even more recently D'Silva et al in the JOURNAL OF LUMINESCENCE 8:375-382 (1974) disclosed that terbium-activated yttrium-gadolinium phosphates were promising candidates for X-ray intensifying screens. When tested against calcium tungstate, europium-activated barium phosphate and terbium-activated gadolinium oxysulfide on blue sensitive film, the terbium-activated yttrium-gadolinium phosphate was found to be marginally superior to the above oxysulfide.
Both of these newer phosphors contain terbium. While in some instances this may be an advantage, e.g., fewer raw materials to handle and keep isolated, etc., terbium is a relatively scarce material and is quite costly.
It is believed, therefore, a blue-emitting X-ray phosphor which does not utilize terbium but which is equivalent to the newer terbium activated phosphors would be an advancement in the art. It is also believed that an X-ray intensifying screen suitable for use in conjunction with standard blue sensitive film would be an advancement in the art. It is further believed that a process for producing such phosphors is an advancement in the art.